With prior railway cars, bulky goods, such as vehicles, were strapped onto the flat railway car in a single level. The unprotected goods were subject to vandalism and theft. These conditions led to the development of auto-rack cars. In auto-rack cars, autos are stacked in two levels. The use of auto-rack cars increased the carrying capacity of railway cars. Furthermore, the goods were enclosed and thus protected.
The A.A.R. has established certain parameters relating to height, width, length, and weight of railway cars. These dimensions cannot be exceeded. For railway cars carrying goods in containers, the size of the containers must also be considered to determine if the railway car falls within the established parameters. The height requirement, in particular, has limited prior railway cars to a two tier arrangement of containers. A third tier could not be accommodated in prior railway cars because of clearance.